Rotating vortex rope formation and mitigation in draft tube of hydro turbines – A review from experimental perspective

Operating hydro turbines in off-design conditions increases the risk of cavitation occurrence, which in turn, leads to numerous problems such as performance degradations, structural vibrations, and most importantly, mechanical damage due to erosion. It is therefore crucial to develop a monitoring system that detects the occurrence and severity of cavitation in real time. For this purpose, a cavitation detection methodology has been developed that is based on the analysis of acoustic emissions of a turbine with machine learning algorithms. In this method, a conventional microphone is used to record the airborne noise emitted from a turbine under different working conditions, and then, a supervised learning algorithm is trained to classify the recorded noise signals into cavitating and non-cavitating categories. The detection system was developed based on laboratory tests and was validated in Ernen hydropower plant located in Canton of Wallis in southeast of Switzerland. This power plant consists of two identical double-flux Francis turbines each having a maximum power of 16 MW and a net head of 270 mWC. The preliminary results obtained from a two-day experimental campaign in the Ernen powerplant are very promising in terms of cavitation detection with a classification accuracy of more than 90 %. The system could be implemented either for real-time monitoring of cavitation occurrence allowing the operators to avoid such a condition or as a post processing tool to evaluate the number of hours a turbine has worked under severe conditions. Work is still ongoing to deploy more complex learning algorithms for this task to minimize expert intervention and/or interpretation during the setup process.

Section: Introductionmentioning

confidence: 99%

Development of a Novel Cavitation Monitoring System for Hydro Turbines Based on Machine Learning Algorithms

Amini

Pacot

Voide

et al. 2022

“…In such conditions, unsteady phenomena such as the formation of dead velocity zones, negative flow, and flow oscillations are observed in the draft tube. Part load (PL) operation (60-90% of BEP), together with highpressure gradient and shear layer separation, results in vortex breakdown and development of the rotating vortex rope (RVR) in the draft tube [2][3][4]. RVR is a low-frequency phenomenon that produces periodic draft tube pressure pulsations [5].…”

Section: Introductionmentioning

confidence: 99%

Repeatability and operational setting of Newly Developed Francis Turbine Test Rig

Kumar

Khullar

Gandhi

2022

Self Cite

A small-scale test rig is developed to study the flow phenomena during off-design operations of a Francis turbine. The test rig can be operated in open and closed loops for a maximum head and discharge of 8 meters and 0.055 m3/s. The runner outlet diameter is 200 mm and rotates at 500 rpm. However, the test rig is not a model turbine test rig as per IEC 600193. Therefore, the repeatability of parameters is the key to establishing reliability in measurement and performance estimation. This paper presents the repeatability results of the turbine unit performed at a constant head. A control system is developed in the LABVIEW program with PID (Proportional, Integral, and Derivative) to run the turbine at the constant head with variable discharge and constant discharge at the variable head.

“…The flow ingested by the draft tube at off-design conditions often has a high residual swirl. This swirling decelerating flow in the draft tube leads to a helical precessing vortex, known as rotating vortex rope (RVR) [4]. This vortical structure precesses the draft axis at about 0.2-0.4 times the runner frequency and leads to severe pressure pulsations and hydraulic losses [5].…”

Section: Introductionmentioning

confidence: 99%

Influence of axial water jet size on RVR mitigation in draft tube of Francis turbine

Khullar

Kumar

Singh

et al. 2022

The present work investigates the effect of the axial water jet nozzle size on the unsteady pressure fluctuations arising from RVR formation in the draft tube of a Francis turbine operating at part load. The results compare two different nozzle diameter jets for their effect on the pressure pulsations and pressure recovery in the draft tube. Simulations were carried out at four jet injections varying from 2% to 10% of the main discharge. The study also presents the changes in the net effective area and average swirl in the draft tube with the introduction of the water jet.